Hearth-ache

Posted on October 25, 2015 by nager

Hearth-ache (n.) /hɑːθ eɪk/

The pain and stresses of trying to work out where to place your stove and constructional hearth in order to comply with impenetrable building standards documents and reams of technical sheets from the stove company.

Matt the architect was effecting a very successful poker-voice on the phone. But I just know he was thinking ‘I told you so’. He might not have said it out loud but I know if I was him I would be singing raucously to myself ‘I told you so i told you so ITOLDYOUSO!’. Fortunately for me, given the misadventures on this project, every professional involved with this project has remained entirely discrete on matters of how they think things are going, and Matt is fortunately of that ilk.

This conversation was an attempt to discover a miracle substance I could use to make my constructional hearth. It had to be an insulator, have a really high compressive strength and also be non-combustible. The internet couldn’t provide me with many ideas. The stove company suggested a mixture of perlite and concrete. But I couldn’t find any figures on how insulating this would actually be.

The first decision, of course, is whether you actually need a constructional hearth in the first place. This depends on the stove, and the temperature that the area under the stove will reach. The stove manufacturer will indicate whether you need a constructional hearth and, for our inset stove, we did. More about choosing the stove here.

And the reason that I would have been chanting ‘told-you-so!’ At top volume if I were Matt? Well it was because in his original designs the concrete floor was laid on top of the insulation. This would have meant that the constructional hearth (at least 250mm non combustible material under the stove) would have had insulation underneath. And cold bridging would not be a problem.

With the insulation and concrete reversed (for the very sensible and pragmatic reason that it was recommended by the builder and it made it considerably easier to get the house built) it was a bit more of a challenge. What I needed was a material that could form part of the constructional hearth but was also an insulator.

Fortunately Matt had an idea – try Foamglas he said. I called the very helpful chap at Foamglas who talked me through the various types and what would be best for my situation.

We decided to get 100 deep Foamglas to maximize the insulation (it has roughly half the lamda value of kingspan) and then allow the screed to fill in the space so it was 80mm thick. A 50mm concrete slab on top of that would give the belt and braces for building control of at least 125mm concrete under the stove.

I bought a box of Foamglas sheets and also a box of Foamglas perinsul- to go under the masonary wall that was to go at the back of the stove. Peninsul has a really really high compressive strength so can go under even load-bearing walls.

An engineer friend was kind enough to do some calculations for me on the back of the envelope and, although he said that Foamglas sheets with a compressive strength of xx would be plenty strong enough to support a masonry wall and certainly the stove, it would be sensible to use the perinsul with a compressive strength of 3200 for under the masonry wall.

The size of the constructional hearth and the superimposed hearth was the other puzzle. The question of using the manufacturers instructions (generally German building standards for a German stove) or Scottish Building Standards. And to confuse event further, the area of the superimposed hearth is not the same as the area and position of the constructional hearth.

I could write reams of utterly boring blurb on calculating the size of the various hearths so I’ll spare you that (there a bit more in this blog). But I’ll tell you that I did read the building standards documents, and the stove technical documents, to within an inch of their lives (I even had to call the German offices of the stove manufacturer to get the answer to a couple of my questions that the stove retailer couldn’t answer) and eventually managed to get my head around them.

In the end I had a plan. It was all a bit time-dependent, as usual, as Builder#1 was about to put the underfloor heating and screed floor in. But, of course, nothing is simple when you are piecing together lots of different builders to do different bits of the build. Builder#3 was to put in the masonry wall that would be behind the stove and mortar down the Foamglas before the floor came in. I called him a few times just to be sure it was all go.

I arrived on site one Monday morning at the very moment that the insulation was going down with a membrane on top, ready for the screed coming in the next day. The first thing I noticed was that the masonry wall was in, with the Foamglas Perinsul underneath, but the Foamglas for the hearth wasn’t there and the Kingspan insulation had already been laid down. The plastic sheet was just being laid down and stapled up the walls ready for the underfloor heating and the screed to come in.

Fortunately it was just in time and they took a saw to the Kingspan and the Foamglas and put it in (phew). The screed came in over the top and then a 50mm concrete slab cut to size went directly under the stove.

That was bit was not without mishap (what isn’t) but it all went in well and now the stove is in and fits and I am glad I went through all the Hearth-ache of working it all out. If anyone else wants to put in a constructional Hearth, I’m your woman to ask…..well perhaps not.

Here’s the definitive blog on the stove

Fired Up, then Burned Out: the excitement and exhaustion of choosing a stove

Posted on October 8, 2015 by nager

It was supposed to be a masonry stove. Being married to a Swiss I’ve spent quite some time in Swiss houses, old and new, that are heated by tiled or plastered masonry stoves. In a tiny and ancient log cabin built by the cow-herds taking their cows to high pasture on the alps, a half-way overnight stop in a meadow in the forest, there was a small tiled stove with a bench to warm your bottom on. In a new house built by parents of our friends, a masonry stove bisected the space in the corner of two rooms and a corridor. Logs were loaded from a door in the corridor, burnt short and hot morning and night, and the heat circulated through a maze of masonry within the walls of the stove kept the house warm all day and night.

Wouldn’t it be lovely to have a masonry stove? A thermal mass in the middle of your home warming from the heart, somewhere warm to snuggle against? So we found a spot right in the middle of the house for the stove and I started on some research. Getting a masonry stove in the UK is evidently rather more challenging than in Switzerland where it is quite standard. I spoke to a couple of people who make stoves, but getting plans for something that would be likely to make it through building control seemed a distant prospect. The process of building control already seemed to be dragging on practically for ever, with waiting for Scotframe to get back to us. I decided to just put in for building control with a basic stand-alone stove made of soapstone so we could at least get started on the building. Then I started looking at alternatives that would give us a stove set into the wall.

I started looking at stoves. An issue was that the space allocated to the stove was quite restrictive and I needed to find a stove that was relatively slim and also and also had the possibility of the flue coming out of the side, so we could keep the flue run going through the cupboard in the upstairs bathroom which had been allocated to it.

It was a bit of an ask but I discovered Spartherm stoves were what I was looking for as they had a heat storage device called a Helix, for taking heat out of the hot flue gasses and storing it. This also meant that the flue could come out of the side of the helix so it would fit into the space allocated for it. I started with a local stove company, The Scottish Stove Company in Croftamie. I needed help on working out the constructional hearth and distances between the stove and the flue as my head was just about popping off with all the complicated guidance and figures. Trying to find out the distance between the centre of the stove and the centre of the flue when attached to the helix was a feat of determination. The distances weren’t on the technical documents for the stove or the helix and, even when I called up the company in Germany (nearly having to enlist the husband to speak German) they couldn’t locate the measurement I was looking for.

So despite me calling the Scottish Stove Company numerous times and popping in a couple, they weren’t really able to answer my questions so I shifted to Kinross Stove company who had the option of an engineer to come out to site which was helpful. I was, by now, at the stage of the build where I had gone from trusting, unquestioning ‘they are all professionals and know what they are doing’ to a position of blossoming control freakery. When I received the diagram from the stove engineer I sent it back twice due to mistakes (firstly a misprint in one of the measurements, and secondly because the sketch assumed we would have the superimposed and the constructional hearth the same sizes, when I had asked for the minimum size of each). I then discovered, when getting Jamie the MVHR fitter to move his pipework slightly to make way for the stove flue, that the stove engineer hadn’t allowed for one of the rafters in the roof SIP panels that was square in the way of the flue run. The flue needed to be at least 50mm from this rafter.

Jamie and I spent a while marking out on the floor the various constraints on where the flue could go: Masonry wall at back, joist at front, rafter in roof to north and extent of cupboard containing the flue to the south. It left a tolerance of 20mm at each side of the flue for where it could go. I went back to the stove technical details, it seemed that it would fit, but I wouldn’t be sure until the stove arrived.

Marked out on the floor – the hatched area is the flexibility for the stove flue
And look! It miraculously fits

When the stove arrived it was massive. It came with two massive guys; Matt from Poland and Verek from the Czeck Republic. They were among the most efficient, practical, polite and effective people I have ever encountered. They’d solved the problem of how to get the hefty stove into the house round the piles of plasterboard on the floor in 10 seconds flat and before I’d even noticed, it was in the house.

I buzzed about them measuring and getting in the way, the amount of thought that had gone into the position of the stove was mind-bloggling so I was determined it went in the right place. The flue didn’t quite fit through the allocated space so Verek got out his angle grinder. Sparks flew.

By the time I had left the flue was through the ceiling and exactly in the position allocated to it (phew!).

The air supply was also attached successfully, to my great relief. While we were doing the foundations the position of the air supply for the stove was a bit of an after thought. The house is very well sealed and has a Mechanical Ventilation Heat Recovery system for ventilation so the stove needs to have its own air supply. The stove burns in its own column of air, sealed from the rest of the house, coming in by pipe under the foundations and going out of the flue. It was almost the last thing that Stuart needed when making the foundations – the question of where the air supply should come out. Eventually it was decided and we sent the plan. But Stuart mistook the position of the flue for where the air supply should come out and it was something I’d been a little worried about ever since. It turned out that, for the stove chosen, this was actually a far more suitable spot for the air supply than the one we’d specified.

The installation went so smoothly and Matt and Verek were brilliant. I had emphasised the importance of sealing up the envelope of the house once the flue went in and it worked perfectly with coordinating with the slater who fitted the flashings and they sealed up all potential for air coming into the house from the outside world.

Altogether, despite the sheer torture and mind-churning preparations and planning I did for the stove, the installation turned out to be calm and smooth-running, apparently free of mishaps. My recommendation to the Kinross Stove Company? Get Matt and Verek to advise on which stoves to fit and sizes and stuff before they arrive to save people like me’s head exploding messily as they try and work it all out from building control manuals and inadequately dimensioned technical drawings.

Masonry Stove

Posted on August 1, 2013 by nager

It might be the best summer we’ve had in Scotland in recent memory and certainly the vision of a legion of sunburned beer bellies parading around the streets of Glasgow will be seared onto my retinas for sometime to come, but it’s time to think about the heating for the House at Cuil Bay.

Today I received the sketches for our masonry stove, so while basking in the sun I am casting up a dreich winter day snuggled on a bench against a heated wall and about to take a hot casserole out of the stove’s oven.

The stove designs have come from from StoveMason, based in Brechin. As far as I could tell (from a brief websearch), he is the only company in Scotland installing masonry stoves.

The reason we are going for a masonry stove as it is something that I have seen work really well in Switzerland where we go regularly to see the in-laws. You not only see beautiful masonry stoves inlaid with tiles in old farm houses, but also modern interpretations in brand new houses and apartments. It is an extremely efficient way of using wood fuel as it circulates the hot air around a maze of bricks inside the stove that absorb and retain the heat rather than it being flushed out of the chimney and lost to the house.

Swiss friends tell me that, rather than burning fuel all the time to keep the house warm, you do a couple of intense burns of wood at high temperature, one in the morning to get the house warm for the day, and one in the evening to heat the house for the night. This method appeals to me because, aside from the environmental benefits, since installing our wood burning stove in our terrace house, finding wood has become a rather obsessive activity, and anything that reduces the demand for wood must be a good thing.

The other appeal is that they are just wonderful. You can have a baking oven, a heated seat or bench, heated walls and a heated panel upstairs as well. We have designed the house with the intention of having the masonry stove right in the centre. It will have a heated wall next to a bench in the hall, an oven for casseroles (bread/pizza? – not sure whether it gets hot enough) in the kitchen and the main part of the stove in the main living area of the house.

If we would be moving there straight away then I think we would consider having the masonry stove as our main source of heat but, given that we will be renting the house out, I think that we will need to complement it with an automated system that needs no human input and that we can operate remotely to ensure the house is warm for holiday arrivals. We haven’t quite decided what this is likely to be, but I can assure you that a blog will follow on this soon enough.